The invention relates to processes for the production of a composite component via multicomponent injection molding, where the composite component comprises a main body composed of a thermoplastic A) and an external layer composed of a foamed thermoplastic B), where the main body is produced in a first process step a) via injection molding of the thermoplastic A) and subsequent hardening of the same in an injection mold, and an external layer is injected on to the main body in a second process step b) which follows directly, via injection molding of a mixture comprising the thermoplastic B) and comprising a chemical blowing agent, and the mixture is subsequently hardened in the same injection mold, with somewhat extended cavity, and the external layer injected on to the main body is foamed in a further process step d) via introduction of heat, and the composite component is solidified via cooling in a final process step e).
The invention further relates to composite components and to reinforced load-bearing elements, where these can be produced by said processes, and also to mixtures, and to the use of said mixtures for the production of composite components.
The design of load-bearing elements, for example the design of bodywork parts for motor-vehicle construction, generally aims to maximize stability, stiffness, and/or load-bearing capability, while at the same time minimizing weight. The load-bearing elements used are therefore often of hollow-profile design, or are hollow, or are at least to some extent of shell-type design. To provide a further increase in the stability of these load-bearing elements, they are often additionally reinforced with reinforcement elements composed of plastic. The literature describes various composite components composed of plastic as suitable reinforcement elements for load-bearing elements.
By way of example, DE 602 14 699 T2 describes structural reinforcement elements which are suitable for the reinforcement of a hollow structural element, and which comprise a reinforcement element which has, on a section of its surface, an expandable adhesive material. Foamable epoxy-based resins are mentioned as preferred expandable adhesive material. A number of processes are mentioned for the production of said reinforcement elements, inter alia two-component injection molding.
J. Kempf and M. Derks, “Karosserie-Leichtbau: Einsatz von Strukturschäumen in Hohlprofilen” [Lightweight bodywork structures: use of structural foams in hollow profiles], in VDI Gesellschaft Kunststofftechnik, Kunststoffe im Automobilbau, VDI Verlag GmbH, Dusseldorf, 2006, pp. 193-205, disclose structural foam parts in which, by way of example, load-bearing items composed of polyamide are produced by two-component injection molding with uncrosslinked structural foam based on epoxy resins. These structural foam parts are then introduced, during the bodywork-construction process, into hollow profiles, and the expansion and solidification of the epoxy foams preferably takes place via exposure to heat in the painting process. A modulus of elasticity greater than 500 MPa at 80° C. is mentioned as one of the requirements placed on the structural foam.
European patent application 08159517.5 (application number), which was not published prior to the priority date of this application, teaches foamable mixtures composed of thermoplastic polyamides and of a copolymer acting as chemical blowing agent. Said mixtures may by way of example be applied by the multicomponent injection molding process to a core material composed of glassfiber-reinforced polyamide, thus producing foamable reinforcement parts. These reinforcement parts can be introduced into hollow profiles and foamed.
These processes described in the prior art for the production of composite components via multicomponent injection molding are not entirely satisfactory in respect of certain properties, and the same applies to the composite components that can be produced by said processes with a foamable or foamed external layer, and more particularly to the composite components described as advantageous and based on foamable epoxy resins. By way of example, when two-component injection molding processes use epoxy resins the high melt viscosity means that either relatively long cycle times have to be accepted or high injection pressures have to be used, both of which lead to increased costs. A further factor is that, when using epoxy resins, it is impossible to achieve the desired extent of computer-aided rheological modeling or optimization of the injection molding process, in order to minimize the need for costly practical trials. The adhesion of the external layer of expandable or expanded epoxy resin to the main body is moreover often inadequate, and the usefulness of the composite component as reinforcement element is therefore restricted. The storage stability and/or resistance to moisture of these known composite components is moreover often also not entirely satisfactory, both in the expandable state and in the expanded state. Recycling of these known composite components at the end of their useful life is desirable but often possible only at considerable cost.